Pacific Electric Ray, Tetronarce californica
Pacific Electric Ray, Tetronarce californica, Male. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, January 2009. Length: 79 cm (31 inches). Disc: 52 cm (20 inches) by 52 cm (20 inches).
The Pacific Electric Ray, Tetronarce californica, is a member of the Torpedo Electric Ray or Torpedinidae Family, and is known in Mexico as torpedo del Pacifico. This fish has historically been known as Torpedo californica but was recently reclassified into the new genus Tetronarce. Globally, there are nine species in the genus Tetronarce, one of which is found in Mexican waters, this species from the Pacific Ocean.
The Pacific Electric Rays have round disc-shaped soft flabby bodies that are smooth, broad, and thick in the front and center and thinner on and behind the sides. They are uniform dark gray to bluish-brown and covered with small black spots dorsally. Their ventral side is off-white. Their head has a very short snout with very small eyes and spiracles. Their mouth is moderately-sized and has small teeth. They have prominent kidney-shaped electric organs that are visible on either side of their head and capable of delivering strong jolts to stun prey, reaching up to 50 volts in larger animals. They also have an accessory electric organ that produces low voltage discharges that may function for communication. Their caudal fin is large and triangular; their first dorsal fin is large; and their tail is short and stocky. Their skin is smooth and devoid of spines.
The Pacific Electric Rays are found demersal intertidally over sandy and rubble terrain at depths up to 1,065 m (3,500 feet, however, they are normally found at depths of less than 200 m (650 feet) and in waters between 10oC (50oF) and 13oC (55oF). They reach a maximum of 1.37 m (4.5 feet) in length and 41 kg (90 lbs) in weight. They are solitary nomadic fish that suspend themselves in water with minimal swimming effort and are more active at night. They primarily hunt prey around rocky reefs and kelp beds and feed on anchovy, halibut, herring, and kelp bass as well as invertebrates. They locate their prey (which is mostly buried in sand) via the electrical stimuli given off by the prey, which they detect through specialized sensory organs, the ampullae of Lorenzini. They are believed to undergo inshore migrations during summer months. During the daytime they rest on the ocean floor partially buried in sand and become ambush predator that lie in wait for their prey. Due to their size and formidable electric shocking capabilities, they have few natural predators. Reproduction occurs via internal fertilization with embryos developing via ovoviviparity and feeding on yolk then via absorption of uterine fluid provided by the mother. Their fecundity rates are high with litter sizes ranging from 17 to 20, however, females do not reach sexual maturity for nine years and the resiliency rate for this species is low. Larger females produce larger litters. Pups are born live as miniature adults that are independent from birth and measure between 18 cm (7 inches) and 23 cm (9 inches) in length. They have a lifespan of between 16 and 24 years. The Pacific Electric Ray is rare and poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Pacific Electric Ray is a resident of Mexican waters of the Pacific Ocean has a limited distribution being found along the west coast of Baja with the fish photographed above establishing the southerly range for this species.
Due to its large stature and uniform brown color, the Pacific Electric Ray cannot be confused with any other species.
From a conservation perspective the Pacific Electric Ray is currently considered to be of Least Concern with stable, widely distributed populations. They are targeted commercially for their electric organs and are currently being evaluated by the biomedical industry for human applications. Ancient Greeks and Romans used the electric current of electric rays to treat aliments such as gout and headaches. They are a minor by-catch of commercial gill net fishermen and commercial shrimp trawlers. Population trends have not been monitored and there is very limited landing data available but it is generally believed that only a limited number are kept each year.
A word of caution. Divers are warned to avoid contact with this ray. Their electric shock is powerful enough to knock down an adult human. They are also known to be very confrontational if harassed and to swim directly towards divers.